Method for the formation of malleable metal powders



United States Patent 3,301,494 METHOD FOR THE FORMATION OF MALLEABLEMETAL POWDERS Erik Tornqvist, Roselle, N.J., assignor to Esso Researchand Engineering Company, a corporation of Delaware No Drawing. FiledMar. 13, 1964, Ser. No. 351,848 11 Claims. (Cl. 241-22) The presentinvention relates to the formation of highly active metallic powders.More particularly, the invention relates to the formation of metallicpowders of malleable metals.

Many ductile or malleable metals that are theoretically quite reactivehave a tendency to be coated by a layer of oxides or other compoundswhen exposed to atmospheric conditions and thus lose their reactivityunder moderate reaction conditions. Metals such as aluminum, magnesium,copper, zinc, etc., have many potential industrial applications but adecrease in reactivity due to coatings with oxides or other compoundsformed as the result of environmental exposure seriously restricts theiruse especially in organic synthesis where only mild reaction conditionscan be tolerated. It is therefore important to remove or at leastpenetrate the layer coating on these metals.

Treatment of malleable metals With halogens, hydrogen halides, alkylhalides, etc., has been suggested for this purpose and is well known tothe art. However, these methods are often not effective and frequentlycause undesirable contamination of the metals as well as consumption ofthe metal. Contamination problems are obviated when the oxide or similarcoating is removed or broken up by grinding or ball milling under inertconditions. However, ball milling in particular has not in the past beensuitable for malleable metals of low or intermediate hardness, as theyform very fine, thin platelets during the ball milling which tends tointerlock or weld and form large clusters that are not suitable forchemical reactions.

Now, in accordance with this invention, it has been found that highlyactive metallic powders of malleable metals that tend to undergo weldingduring milling can be prepared by attriting the same in the presence ofsuitable metal halide salts. Following the attriting operation, themetal halide salt grinding aid is separated from the metallic powder byemploying conventional extraction, reaction-extraction, sublimation, ormechanical separation techniques, the latter making use of thedifference in physical properties between the metal and the halide. Thesolvents and/or reactants that are employed in the separation operationshould be inert to the metals under the conditions used for theseparation. The metal halide grinding aids employed in the process ofthe present invention prevent agglomeration of the metal powder and alsoserve as reactive abrasives, thus aiding the removal of the coating onthe metal surface. As a result, the metals treated in this manner show amuch higher reactivity than those treated according to previously knownmethods and can be used for carrying out reactions which have hithertobeen considered impossible.

The malleable metals that can be treated according to the process of thepresent invention are those which normally weld together or interlockwhen subjected to a milling or grinding treatment without the presenceof the grinding aids of the present invention. The metals that areespecially suited to the process of the present invention have a Brinellhardness in the range of from about 1 to 75 and include metals such as:Zinc, indium, lead, tin, aluminum, cadmium, gold, silver, magnesium,platinum, copper, palladium, iron, as well as malleable alloys such asmagnesium and aluminum, zinc and aluminum, copper and magnesium, and tinand lead. A compila- Patented Jan. 31, 1967 tion of malleable metalswith Brinell hardness information can be found in The Metallurgists andChemists Handbook, 2nd Edition, compiled by D. M. Liddell, McGraw- HillCo., Inc., New York, 1918, p. 193. Metals having a Brinell hardnessgreater than 75, such as, for example, nickel, zirconium, beryllium, andcobalt can be ball milled without the presence of the grinding aids ofthe present invention to form finely divided powders.

The grinding aids employed in the process of the present inventionpreferably have metal moieties that are at least as electropositive asthe metal being milled, i.e., they are either metal halidescorresponding to the metals being ground or metal halides, the metalmoieties of which are more electropositive than the metals being milled.For example, AlCl could be used in the formation of aluminum powders aswell as in the production of powders of zinc, cadmium, tin, etc.However, under certain conditions it is also possible to use as thegrinding aid a metal halide of a metal which is slightly lesselectropositive than the metal to be activated. Some contamination ofthe original metal by the metal of the halide will then generally occur,but this contamination may not always be harmful, especially if it israther minute as will be the case when the two metals differ onlyslightly in electropositive character. Thus AlCl which is a particularlysuitable grinding aid, may be useful for activating magnesium if aslight contamination of the final reaction products with aluminum can bereadily tolerated. In general, the most reproducible results areobtained when anhydrous, solid, metal chlorides and bromides of GroupsII-A, II-B, III-B, IV-A, IV-B, V-A, V-B, VI-A, VII-A and VIII of theMendeleev Periodic Table in which the metal is in its lowest valencestate are employed. Salts of metals of Groups LA and IB can be used asgrinding aids; however, these salts are not readily separated from amixture of the salt and the metal being ground. Salts such as aluminumchloride, aluminum bromide, zinc chloride, zinc bromide, magnesiumchloride, magnesium bromide, stannous chloride, stannous bromide, leadchloride, lead bromide, and ferrous chloride are particularly preferredas grinding aids in the process of the present invention.

The attriting operation involving the metal being activated and thegrinding aid is preferably conducted in the absence of a diluent;however, diluents can be used. The presence of a diluent during grindingoperations generally serves to diminish grinding etficiency, thus makinga longer period of grinding necessary for obtaining a desired degree ofactivation and, additionally, the diluent usually has to be removed fromthe metal powder product after the grinding operations have beencompleted and thus presents separation problems. Furthermore, it hasbeen found that powders dry ball milled according to this invention aremore reactive than those obtained after milling in the presence of adiluent.

After the grinding operation has been completed, the grinding aid can beseparated from the metallic powder by employing any one or a combinationof a wide variety of techniques. For example, the metal halide grindingaid can be removed from the mixture of grinding aid and metal powder bysublimation. In a similar manner, the metal halide grinding aid can bereacted with an alkyl metal compound to form a more volatile productwhich is then removed from the activated metal powder by evaporation,e.g., distillation or sublimation. Additionally, the metal halidegrinding aids can be removed from a mixture of grinding aid and metalpowder by contacting the mixture with an extractant having an aflinityfor the grinding aid. Representative examples of such extractant arearomatic hydrocarbons, diphenyl ether, dioxane, and certain tertiaryamines. Particularly useful amines-are triphenylamine and trialkylamineswherein each alkyl group has from 2 to 7 carbon atoms. Followingcontacting with the inert solvent the metal powder is removed from thetotal mixture by filtration, decantation or centrifugation.

Another effective method for the separation of the grinding aid from themetal powder because it can be used for the separation of a wide varietyof metal halide compounds involves contacting the mixture of grindingaid and metal powder with an alkyl metal compound that will react withor complex with the metal halide of the system to form products solublein suitable inert solvents. With this method the total mixture is thencont-acted with a diluent that will solubilize the reaction product orcomplex, whereupon the mixture is filtered, decanted or centrifuged,possibly with additional diluent washing, and a highly reactive metalpowder substantially free of grinding aid is obtained. Particularlyvaluable alkyl metal compounds are the alkyl aluminum compounds having 2to 8 carbon atoms per alkyl group. Representative examples of usefulalkyl aluminum compounds are trialkyl aluminum compounds such astriethyl aluminum, tripropyl aluminum, triisobutyl aluminum, and thelike, and also dialkyl aluminum compounds such as the diethyl aluminumhalides, e.g. diethyl aluminum chloride, dipropyl aluminum chloride,diisobutyl aluminum chloride, and the like. The inert diluent suitableas wash liquids include C to C straight or branched chain hydrocarbonssuch as n-hexane, n-heptane, isooctane, and n-decane, cycloparaffinssuch as cyclohexane and methyl cyclohexane, aromatic hydrocarbons suchas benzene, toluene, Xylene, ethyl benzene, etc.

The dry milling process is carried out by placing the malleable metal tobe activated and the metal halide grinding aid in a ball mill, a pebblemill or another suitable grinding device and then milling the metalhalide and malleable metal in the absence of diluents in an inertatmosphere, such as a nitrogen or argon atmosphere which issubstantially free of oxygen and water vapor, for a period of timesufiicient to substantially attrite the malleable metal. Effectivegrinding can normally be secured when the molar ratio of malleable metalto metal halide grinding aid present in the grinding zone lies in therange of from about 1:1 to 1. -However, the most efficient activation isusually obtained when the molar ratio of malleable metal to metal halidegrinding aid present in the grinding zone lies within the range of fromabout 3:1 to 12:1.

The optimum time period for the dry milling operation depends in generalupon the efliciency of the equipment used, the malleable metal beingground, the grinding aid used, the ratio between metal and metal halide,and the degree of attrition (activation) desired. To obtain a powder ofa malleable metal in which the major portion of the particles is withinthe size range of from about 0.1 to 20 microns, ball milling times offrom about 0.2 hour to days can be used. However, times ranging from 0.2to 10 days will be more common. The time period most suitable for anygiven attriting equipment can, of course, be easily determined byroutine experimenta tion.

The pressure at which the milling operation is conducted is notcritical; however, the temperature used should be well below the meltingpoints of the malleable metal and the grinding aid so as to preventfusion of the two components. Temperatures in the range of from about 0to 100 C. are commonly used. The temperatures at which the grinding aidis removed from the mixture of grinding aid and metal powder will ingeneral depend upon the method of separation used, the diluents used,and the nature of the grinding aid. Preferably, temperatures in therange of from about 10 C. to 400 C. can be used; however, temperaturesin the range of from about 10 to 250 C. are preferred.

The grinding operation of the present invention can be conducted eitheras a batch or as a continuous process.

While the desired attrition of the malleable metal may be obtained byuse of tight steel rolls or jet impact, attrition, the use of heavy ballmilling is preferred as the amount of attrition desired is usually verysevere. In ball milling operations utilizing either conventional ballmills or swinging mills, it is advantageous to use steel balls or someother suitable high density grinding media having a specific gravity ofat least 7. However, less dense grinding media such as flint pebbles canalso be used for obtaining highly activated metal powders if longermilling periods are utilized. Generally, the balls used should be largeenough in diameter to give high shearing intensity; however, the size ofthe balls is not too critical since smaller balls give more collisionsand this partly makes up for the difference in ball diameter. Thus, inlaboratory ball mills having a volume of from about 1 to 10 liters, onemay advantageously use steel balls of A to 1 in diameter, while incommercial operations larger sizes, such as up to 2" in diameter, areusually preferred.

The activated powders of malleable metals having Brinell hardnesses inthe range of from about 1 to 75 as produced by the process of thepresent invention have many varied uses. For example, aluminum powderthat has been activated by ball milling in the presence of aluminumchloride is so active that it readily reacts with chlorobenzene to makephenyl aluminum chloride, whereas aluminum that has not been subjectedto the process of the present invention will show little or no reaction.Additionally, magnesium ground in the presence of magnesium chloride oraluminum chloride will readily react with alkyl halides in the absenceof ether to make ether free Grignard reagents, whereas the nonactivatedmagnesium will not react in the absence of ether. Furthermore, aluminumand copper powders as prepared by the process of the present inventionreadily react with titanium tetrachloride in a substantially aromaticdiluent under very mild conditions to form nearly quantitative yields oftitanium trichloride cocrystallized with either aluminum chloride orcopper chloride. These materials are excellent catalyst components forthe formation of solid polymers of alpha olefins.

This invention and its advantages will be better understood by referenceto the following examples:

Example 1 Seven activated nAl-AlCl mixtures were prepared by milling thecomponents together in stainless steel jars with chrome alloy steelballs as the grinding medium. The composition of the charges and themilling conditions are shown in Table I. Finely divided powders wereobtained in most cases but as indicated in the table, while four days ofball milling a 12Al1AlCl mixture (Run 1) resulted in the formation of afinely divided aluminum colored product, 14 days of milling the samemixture (Run 2) resulted in severe caking and in the formation of aconsiderably darker product. Fourteen days of ball milling an 8Al1AlClmixture in a 2.5 1. jar also resulted in appreciable caking (Run 3)while milling of the same mixture for the same time in a 7.7 1. jarresulted in only slight caking (Run 4). Very dark products having acolor approaching that of finely divided iron powder were obtained inboth cases. The finely divided products from milling 6Al1AlCl (Run 5),5Al1AlCl (Run 6) and 3Al1AlCl (Run 7) were also considerably darker thanthe starting materials.

The pronounced deepening in color indicated the changes happening duringthe grinding, since milling of aluminum powders according to previouslyknown techniques has always yielded powders of a color typical foraluminum. Particularly surprising was the dark color of the 5Al1AlCl and3Al1AlCl preparations, since these contained 50 and 62% of colorlessAlCl respectively. However, this observation became less surprising onceit had been established that the grinding had a unique effect, sincethese preparations were milled under metal particles without anyapparent attrition taking place. Runs Nos. 6 and 7 illustrate thenecessity of the TABLE I.ACTIVATION OF ALUMINUM BY BALL MILLING WITHA1013 Run -4-.- 1 2 3 4 5 6 7 Charge:

Aluminum Powder, g.= 324 324 I 324 1,296. e24 R10 486. A101 g 133.4-133.4- 2m 8011 266.7- 800 800. Al/AlCla Molar Ratio 1 12 8 8 6 5 3.Milling Conditions: Y

Grinding Medium Chrome Alloy Steel Balls Jar Size, 1. 2.5- 2.5- 2.5..7.7- 2.5- 7.7- 7.7. Time, days. .4 14 14 14 .14 14 14. Color of ProductAluminum.. Dark Very dark, Very dark, like Dark bluish, Very dark,Lighter 1 metallic. slightly iron powder. metallic. almost like than 6.

. lighter iron powder. than 4; Remarks Caked Caked Slight caking.

\\ Alcoa #123, average particle diameter, 16 microns.

b After the cake had been broken up, 66.7 g. AlOl was added to the jarto bring the Al/AlCla ratio to 8 and the milling continued. No cakingtook place during the first 4% hours of grinding, but it had occurredafter 7 hours.

B 200 g. of the caked material were brokenup and charged to a 1.021.steel jar and milled for 2 hours. This yielded a finely divided powdercontaining only a few small lumps.

.After the grinding operation, substantially pure, actistirring over aperiod of 8 minutes 400 m1. of dry n-heptane containing 76.1 grams ofdissolved triethyl aluminum. During the period when the triethylaluminum was added to the reaction flaskthe temperature of the flaskrose from 26 to 36 C. due to the reaction between the aluminum chlorideand triethyl aluminum. The reaction mixture'was then stirred for 1 hourwhereupon it was filtered in a dry box. After washing with severalportions of dry n-heptane and drying in vacuo on a steam bath, aquantitative yield of substantially pure activated aluminum powder wasobtained.

Example 2 I i To illustrate the general effectiveness of the grindingmethod of the present invention for preparing a wide variety ofactivated metal powders ofmalleable metals,

six different metals were ground with varying amounts of; aluminumchloride. The results of the tests and the conditions at which they wereeffected are setforth in Table II below.

"the metal to aluminum chloride mole ratio was 12, a

presence of a grinding aid when powders of malleable metals are desired.In Run No. 6 wherein the mole ratio ofv metal to aluminum chloride was6, a finely divided powder was obtained, whereas in Run No. 7 whereincake of tin and aluminum chloride was obtained.

Example 3 v i To further demonstrate the general effectiveness of themetal grinding method of this invention, 339 grams of zinc powder. and35.2. grams of anhydrous zinc chloride were placed in a gallon stainlesssteel jar and milled with chrome alloy steel balls under inert-conditions for five days.

After completion of the milling, a very finely divided powder wasobtained from which the zinc chloride could be removed -by AlEtg-Tlheptane washing analogous to the method described in Example 1.

- Example 4 The following experiment was conducted to demonstrate theextremely high reactivity of metal powders prepared in accordance withthe method of the present invention. A 4-necked, 2-1iter reaction flaskequipped with stirrer, reflux condenser and thermowell was chargedinside a nitrogen-containing dry box with the following reagents: 189.7g. (1 mole) TiCl 9 g. /s atom) aluminum powder prepared according toExample 1, Run 1, and 750 ml. of dry benzene.

cooled with ice in order to avoid boiling of the benzene diluent beforethe flask and its auxiliary equipment TABLE II Ag Mg Zn Cd Sn Sn 323. 72 91. 6 784. 6 337. 2 256. 1 256. 1 33. 4 133. 3 133. 3 66. 7 66. 7 33.4 12 12 12 6 6 12 M M M M M M v 3 4 4 3 3 3 Q) G) (F) Finely dividedpowder. 7 Cake.

As is indicated by the data in Table II above, excel lent milling wasobtained in all cases where a suflicient amount of aluminum chloridegrinding aid was present. The presence of the grinding aid served bothto reduce the metal particle size and to form clean, oxide-free metalsurfaces. The above results contrast sharply with the poorer resultsobtained in milling experiments wherein pure metals were ground withoutthe presence of a grinding aid and either caking (cluster formation)occurred could be set up in a hood. In spite of the ice cooling thetemperature rose to 64 C. in 7 minutes. The stirred andnitrogen-blanketed flask was heated to 81.5 C. within 20 minutes and themixture was refluxed for 1 hour. The contents of the flask were thenfiltered in a dry box, thoroughly washed with n-heptane and dried invacuo. A yield of 184.2 g. of a cocrystalline material having thecomposition TiC1 -0.33A1Cl and the structure of beta-TiC1 was obtained.The yield obtained or rather large platelets were formed from theoriginal was essentially quantitative considering that the theo- Astrongly exothermic reaction started immediately and the flask had to beretical yield is 198.7 g. and that minor losses took place during therecovery procedure.

By contrast, the use of commercial aluminum powder (Alcoa #101 or 123).did not result in more than a 10 to 20% yield even when refluxingperiods as long as 12 to 15 hours were used.

Example 5 An activated 12A1-1A1C1 mixture was prepared by milling 927grams of aluminum powder and 400 grams of aluminum chloride with flintpebbles in a 1- gallon porcelain jar for 17 days. Substantially pureactivated aluminum powder was then obtained from this finely-dividedmixture by washing the mixture with triethyl aluminum and n-heptaneaccording to the method described in Example 1.

Example 6 8 sisting of chlorides and bromides of metals of Groups II-A,II-B, III-B, IV-A, IV-B, VA, V-B, VI-A, VILA, and VIII of the MendeleevPeriodic Table, the metal moiety of said metal halide grinding aid beingat least as electropositive as the malleable metal being ground,contacting the mixture with an extractant having an afiinity for saidgrinding aid, and recovering a powder of said malleable metalsubstantially free of said grinding aid.

4. The method of claim 3, wherein the extractant is a trialkylamine,each alkyl group of said amine having from 2 to 7 carbon atoms.

5. The method of claim 3, wherein the extractant is a triphenylamine.

permitted to cool to room temperature and 26.8 grams of substantiallypure highly reactive aluminum powder were recovered.

The advantages of this invention will be apparent to those skilled inthe art. Highly active powders of malleable metals can be directlyprepared by the process of the present invention. It is to be understoodthat this invention is not limited to the specific examples set forthherein, which have been oifered merely as illustrations, and thatmodifications may be made without departing from the spirit and scope ofthe appended claims.

What is claimed is:

1. A method for producing powders of malleable metals which comprisesseverely grinding in the absence of a diluent, a non-fused mixtureconsisting essentially of at least one malleable metal having a Brinellhardness ranging from about 1 to 75 and at least one solid metal halidegrinding aid selected from the group consisting of chlorides andbromides of metals of Groups II-A, II-B, III-B, IV-A, IV-B, VA, VB,VI-A, VII-A, and VIII of the Mendeleev Periodic Table, the metal moietyof said metal halide grinding aid being at least as electropositive asthe malleable metal being ground, and recovering a powder of saidmalleable metal substantially free of said grinding aid.

2. The method of claim 1, wherein the metal halide grinding aid is ametal chloride.

3. A method for producing powders of malleable metals which comprisesseverely grinding in the absence of a diluent a non-fused mixtureconsisting essentially of at least one malleable metal having a Brinellhardness ranging from about 1 to 75 and at least one solid metal halidegrinding aid selected from the group con- 6. A method for producingpowders of malleable metals which comprises severely grinding a mixturecomprising at least one malleable metal having a Brinell hardnessranging from about 1 to and at least one solid metal halide grindingaid, contacting said mixture with an alkyl metal compound having atleast two alkyl groups per molecule to react said grinding aid with saidalkyl metal compound, washing said mixture with a diluent having asolvent aflinity for said reaction product of said grinding aid and saidalkyl metal compound, and recovering a powder of said malleable metalsubstantially free of said grinding aid.

7. The method of claim 6, wherein said alkyl metal compound is an alkylaluminum compound.

8. The method of claim 6, wherein said alkyl metal compound is an alkylaluminum compound, said compound having from 2 to 8 carbon atoms peralkyl group and said alkyl aluminum compound is present in amountssufiicient to react and completely solubilize substantially all of saidgrinding aid.

9. The method of claim 6, wherein said washing diluent is an aliphatichydrocarbon liquid having from 5 to 12 carbon atoms per molecule.

10. A method for producing aluminum powder which comprises ball millinga mixture comprising aluminum and aluminum chloride for a period of fromabout 0.2 hour to 30 days, contacting said mixture with triethylaluminum in amounts sufficient to react and substantially completelysolubilize the aluminum chloride of said mixture, washing said mixturewith n-heptane, and recovering aluminum powder substantially free ofaluminum chloride.

11. A method for producing aluminum powder which comprises ball millinga mixture comprising aluminum and aluminum chloride for a period of fromabout 0.2 hour to 30 days, heating said mixture for a time suflicient tosublime at least a major portion of said aluminum chloride, andrecovering aluminum powder substantially free of aluminum chloride.

References Cited by the Examiner UNITED STATES PATENTS 2,984,560 5/1961Dombroski 75-.5 3,090,567 5/1963 Schafer 241-22 3,129,896 4/ 1964 Heins241-22 3,176,925 4/1965 Huband 241-22 X ANDREW R. JUHASZ, PrimaryExaminer. H. F, PEPPER, Assistant Examiner.

1. A METHOD FOR PRODUCING POWDERS OF MALLEABLE METALS WHICH COMPRISESSEVERELY GRINDING IN THE ABSENCE OF A DILUENT, A NON-FUSED MIXTURECONSISTING ESSENTIALLY OF AT LEAST ONE MALLEBLE METAL HAVING A BRINELLHARDNESS RANGING FROM ABOUT 1 TO 75 AND AT LEAST ONE SOLID METAL HALIDEGRINDING AID SELECTED FROM THE GROUP CONSISTING OF CHLORIDES ANDBROMIDES OF METALS OF GROUPSII-A,II-B,III-B,IV-A,IV-B,V-A,V-B,VI-A,VII-A, AND VIII OF THE MENDELEEVPERIODIC TABLE, THE METAL MOIETY OF SAID METAL HALIDE GRINDING AID BEINGAT LEAST AS ELECTROPOSITIVE AS THE MALLEABLE METAL BEING GROUND, ANDRECOVERING A POWDER OF SAID MALLEABLE METAL SUBSTANTIALLY FREE SAIDGRINDING AID.